painting to cool house

• posted on May 2, 2005, 9:07 am
Does painting the outside walls of a house white help much to keep it cool? Do people living in the desert tend to have light houses?
thanks Laura
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• posted on May 2, 2005, 10:11 am

Dark colors do absorb heat more than light. Good insulations is also important.
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• posted on May 2, 2005, 10:32 am
If you are in the desert area yes. at 30f something black can be 40 f warmer than something white measured with an IR thermometer. Do your own test by an Infra.Red. thermometer at Radio Shack
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• posted on May 3, 2005, 10:32 am
Thanks for the answers! I didn't mean to imply I live in the desert, I'm in NY State. It gets hot and muggy here in the summer. I don't think that the sun in the winter does much to heat up the house because the sunshine is so weak & mostly cloudy days. My house is pretty dark on the outside - roof and exterior walls are dark - I've been wondering how much the dark walls contribute to baking me in the summer :) Steaming, more like.
Laura
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• posted on May 2, 2005, 10:44 am

On a 90 F day, 1 ft^2 of R20 light-colored wall outside 80 F air would gain (90-80)1ft^2/R20 = 0.5 Btu/h. A dark wall in full sun might have 250 Btu/h = 0.1741x10^-8((T+460)^4-(90+460)^4), so T = 236 F, and (236-80)/1ft^2/R20 = 7.8 Btu/h, eg (7.8-0.5)8x40 = 2340 Btu/h more for an 8'x40' wall.

They should, but some "planned communities" in Arizona specify _maximum_ reflectivities for walls and roofs, based on aesthetics... :-)
Nick
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• posted on May 2, 2005, 11:12 am
Lacustral wrote:

Andy writes:
Generally speaking, yes. The more "heat" you can reflect from the surface of the house, the less is absorbed into the structure which heats the inside. A reflective metal roof will do wonders, also.
But bear in mind that the opposite occurs in the winter, when it would be nice to absorb all the heat from the sun and the surrounding that you can. I understand that the desert gets really cold in winter, and you generally have to use more energy to heat up something than to cool it off a few degrees, since there is a mechanical advantage in BTUs of cooling, but you usually have to burn something to heat.......
So, whether or not a really reflective dwelling is a good idea depends pretty much on where you are located and the summer/winter sunshine characteristics..
If you were to "re-paint" and "re-roof" twice a year, it might work pretty good, but I haven't heard of anyone actually using this fantastic idea of mine.... :>)))))
If you shade your house with trees, you can accomplish the same thing, and the neighbors won't mind...... Oops, I mean shade your house with cactusseses.... :>))))
Andy
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• posted on May 2, 2005, 12:42 pm

Since he would only need to heat the house at night, it really wouldn't matter what the color of his house is, however.
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• posted on May 2, 2005, 12:58 pm

Maybe plants that lose their leaves in wintertime, eg grapes on a trellis, over a dark wall...
Nick
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• posted on May 2, 2005, 4:56 pm

Often done in some parts of the country. Of course in the desert they can't grow a big oak tree. East and South sides of the house have trees that will lose leaves in the winter but give shade in the summer. Evergreens are planted on the other sides to block the prevailing winds.
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• posted on May 2, 2005, 5:25 pm
wrote in message

Live Oaks and Mexican Blue Oaks do well where I am in El Paso, Texas. Where they are legal, the classic shade tree in the desert is the Mulberry.
Matthew
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• posted on May 2, 2005, 8:30 pm
Matthew wrote:

Is this the tree that grows about 30-40 ft tall and has a redish-purple fruit (http://en.wikipedia.org/wiki/Mulberry)?
Why would a Mulberry tree be illegal?
Jeff
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• posted on May 2, 2005, 9:00 pm

they are illegal, along with olive trees, here in the phoenix area. they are incredibly prolific pollen producers, causing widespread allergy problems.
regards, charlie cave creek, az
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• posted on May 2, 2005, 9:12 pm

a fruitless variety with a little darker leaves. New plantings are illegal in my city and many others in the Southwest (USA) because they cause an allergic reaction in many people.
Matthew
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• posted on May 2, 2005, 11:39 am
Lacustral wrote:

Yes and yes, but don't expect too much.
There is a larger effect for those living in a desert type area, and remember if you live in an area that requires heating a good part of the year, the reverse is also true.
I would look especially to the roof color. While a properly vented roof will reduce the direct heat gain to the house a light roof will help keep the roof itself cooler and help it last longer.
--
Joseph Meehan

Dia duit
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• posted on May 2, 2005, 12:25 pm

Beyond the other responses, the website for the county that I live in recommends shading your outdoor A/C compressor with a tree.
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• posted on May 2, 2005, 12:56 pm

White and pastel colors tend to reflect the heat and keep the interior cooler. How much depends on many factors, although there is little difference. A shade tree will have a much greater impact.
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• posted on May 2, 2005, 9:15 pm
I suggest you want an overhang on the south side of your house with windows.
In the summer, when the sun is high in the sky, the overhang will shade the windows. In the winter, the sun is lower in the sky and the sun can shine through the windows.
You want to shade the east and west sides in the summer.